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The Mystery of the Stranded Pups

We now have a better understanding of why sea lion pups began stranding themselves on Santa Monica Bay beaches last year, writes staff scientist Dana Murray.

An emaciated sea lion pup looks lost on a Santa Monica beach. Lying motionless near the shore, he doesn’t look like he’s doing very well. The pup’s bony spine and ribs are visible through his tan skin. Concerned passers-by wonder why he isn’t with his mother. Feeling helpless, they ask what can be done to help this poor animal.

This disturbing scene was a far-too-common sight last spring on our shorelines. Hundreds of sea lion pups, babies younger than a year old, found themselves isolated and starving on our beaches. The National Oceanic and Atmospheric Administration would declare the strandings an “unusual mortality event,” or “UME,” in Southern California.

After months of mystery, we now have a better idea of what caused this unfortunate event.

This past week NOAA released the results of their research, which indicates that the large number of stranded, malnourished pups can be attributed in part to a decrease in the availability of prey for nursing mother sea lions, specifically sardines. Lack of high quality, close-by food sources was the culprit – not disease, or radiation from Fukushima (as some might have speculated).

Indeed, evidence shows that sardine spawning grounds shifted further offshore locally in 2012 and 2013, making it harder for mama sea lions to catch their food. Many female California sea lions couldn’t provide adequate milk to nourish their pups, resulting in premature weaning. However, NOAA is still investigating other causes as well.

Stay tuned for more information as it develops. And a reminder: if you do encounter seals or sea lions on our shores this summer, remember to keep people and pets at least 100 feet away from the animal. Do not pour water or sand on the sea lion. You can call local marine mammal rescuers at 310-458-WILD.

During the previous stranding, Heal the Bay fielded dozens of calls from the public and networked with our many partners to help out.

Facilities such as the Marine Mammal Care Center in San Pedro soon became full of these baby sea lions. A few months later, other animals such as elephant seals had no space to go for rehabilitation when they started showing up sick and injured. As a result, Heal the Bay worked with major donors and foundations to help fund the construction of a new facility for injured and sick elephant seals at the California Wildlife Center in Malibu.